/Engine/Source/Runtime/Slate/Public/Framework/Application/SlateApplication.h
Takes a screenshot of the widget writing the results into the color buffer provided, this version allows you to provide an inner area to screenshot. Note that the format is BGRA. The size of the resulting image is also output.
true if taking the screenshot was successful.
bool TakeScreenshot ( const [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > & Widget, const FIntRect & InnerWidgetArea, [TArray](API\Runtime\Core\Containers\TArray)< [FColor](API\Runtime\Core\Math\FColor) > & OutColorData, FIntVector & OutSize )